1. Field of the Invention
This invention relates to soil moisture indicators and particularly to soil moisture indicators that are completely passive and are particularly suited for use in potted plants.
2. Description of the Prior Art
U.S. Pat. No. 3,019,638 and 3,824,844 (73/73) disclose soil moisture monitors which in construction and operation are different from the present invention but which are intended to achieve a purpose generally similar to that achieved by the present invention.
U.S. Pat. No. 3,881,873 (23/253 TP) discloses a moisture indicating probe and a method of use which also is designed to achieve the same purpose as the present invention but which employs completely different principles of operation.
More than a year before the filing date hereof there has been on sale in the United States of America a device composed of a rigid body having sufficient strength to afford insertion thereof into soil and a water sensitive sub-assembly adhesively secured to said rigid member that is composed of a central layer of blotter paper laminated on opposite surfaces with congruent transparent sheets. The transparent sheets are glued to the blotter paper and the lower transparent sheet is in turn glued to the rigid body. The devices that have been on sale operate satisfactorily when new but have a relatively short life because the blotter paper, particularly when it is wet, tends to delaminate so that the device is subject to delamination. Delamination is likely to occur upon insertion of the device into the soil surface.